1. Field of the Invention
This invention relates to a method for increasing the operating efficiency of expansion turbines, providing more shaft power per pound of working fluid throughput. More particularly, this invention relates to a method for increasing turbine efficiency wherein increased condensation of the working fluid is accomplished without excessive vibration or turbine blade damage.
2. Description of the Prior Art
The use of power recovery turbines to harness the energy of waste heat streams has increased significantly as a result of escalating fuel costs. There have been many attempts to increase the reliability and efficiency of expansion turbines. Generally, the prior attempts have focused on corrosion control, turbine lubrication and improved Rankine cycle working fluids.
U.S. Pat. No. 3,991,603 teaches turbine damage due to induction of water into a turbine and a method to detect the presence and quality of moisture in the vapor flow of steam turbines. U.S. Pat. No. 4,237,691 teaches chemical corrosion control in steam turbines by the removal of water soluble impurities from the working fluid of a steam turbine. Belgium Patent 558,194 teaches chemical corrosion control by the introduction of ammonia derivatives into the working fluid and German Patent 874,451 teaches a corrosion reduction process which prevents salts from reaching the turbine blades. U.S. Pat. No. 1,666,523 teaches corrosion reduction by providing alkali nuclei around which moisture can form thereby diluting active corrosive materials introduced into the turbine to an extent that corrosion is reduced.
British Patent 135,452 teaches the injection of heavy mineral cylinder oil or equivalent grease into the steam service to reduce turbine blade corrosion. U.S. Pat. No. 2,642,722 teaches the use of any alkyl acid phosphate to temporarily emulsify the water present, thereby providing preferential wetting and lubrication by a refined low viscosity oil supplied in the steam service. U.S. Pat. No. 3,834,166 teaches the use of alkylated aromatic hydrocarbons as lubricants in expansion turbines. U.S. Pat. No. 3,603,087 teaches the use of dual Rankine cycle fluids wherein one fluid such as water is used as the working fluid and another fluid such as glycol is used as the lubricant.
U.S. Pat. No. 3,722,211 teaches a Rankine cycle working fluid of trifluoroethanol containing about 1 to 40 weight percent water. U.S. Pat. Nos. 3,841,099 and 4,232,525 teach the use of water-pyridine mixtures and tetrafluoropropanol-water mixture, respectively, as Rankine cycle working fluids. U.S. Pat. Nos. 3,516,248 and 4,132,075 teach use of a number of organic working fluids in a Rankine cycle system. French Patent Publication 2,112,778 and Dutch Patent Publication 7,613,168 teach the use of a silicon bromide-iodide mixture and an azeotropic mixture of methoxypropanol and water, respectively, as working fluids for turbines.
The aforementioned systems are not capable of increasing the efficiency of conventional power recovery turbine systems. Generally, the working fluid in power recovery turbines is a process stream such as high pressure steam. The prior art has recognized the disadvantages of water condensation in steam turbine working fluids and the resultant turbine blade damage and vibration resulting therefrom. In power recovery systems one does not have the flexibility to choose a more efficient direct working fluid, without a dual system involving heat exchange.